EQ: What is chemical and mechanical weathering? Rocks and Weathering EQ: What is chemical and mechanical weathering?

Weathering Weathering – process that breaks up rocks and other substances at the Earth’s surface Two types of weathering, mechanical and chemical Heat, cold, water, ice, oxygen and carbon dioxide contribute to weathering Erosion – movement of rock particles by wind, water, ice or gravity

Mechanical Weathering Mechanical weathering – rock is physically broken into smaller pieces Caused by heating and cooling, freezing and thawing, growth of plants, actions of animals, and abrasion Abrasion- grinding away of rock by rock particles carried by water, ice, wind or gravity Works slowly , over long periods of time. Eventually wears away whole mountains

Mechanical Weathering Ice wedging Occurs in cold climates Water seeps into a crack in the rock, freezes (expands)and thaws (contracts) repeatedly This process expands the rock slowly and pieces crack off

Chemical Weathering Chemical Weathering – process that breaks down rock through chemical changes. Agents are water, oxygen, carbon dioxide, living organisms, and acid rain Produces a different mineral makeup from the rock they came from i.e. – granite begins with minerals of feldspar, quartz and mica. After chemical weathering, granite changes feldspar to clay http://www.classzone.com/books/earth_science/terc/content/visualizations/es1202/es1202page01.cfm

Chemical Weathering Creates holes or soft spots in the rock allowing it to break apart more easily Chemical and mechanical weathering often work together. Mechanical weathering breaks apart rock This process exposes more surface area of the rock to chemical weathering

Five agents of Chemical Weathering Water – most important agent of chemical weathering. Wears away rock by dissolving the rock, mixing it uniformly to make a solution Oxygen – combines with iron in the presence of water. This is oxidation. Causes rust. This process makes the rock crumbly and gives it a red or brown color

Five agents of Chemical Weathering Carbon Dioxide – found in our air. Dissolves in water and forms a weak acid called carbonic acid. Weathers marble and limestone Living organisms – as plant roots grow they produce a weak acid that slowly dissolves rock around the roots Acid Rain – cause is burning fossil fuels that pollute air with sulfur, carbon, and nitrogen compounds. The compounds mix with cloud vapor to form acid.

Rate of Weathering Two factors that determine the rate Type of Rock – Depends on the minerals that make up the rock Is the rock permeable – full of tiny, connected air spaces that allow chemicals to seep through it Climate Average weather conditions of an area Hot and wet climates weather rock more quickly

Class Work and Homework Fill In What did I learn Confused Say Rock Shake Page G46 Read pages G 40 – G 45, #’S 1-5